1. Field of the Invention
This invention relates to a guide roller device for the conveyor belt of a belt conveyor that prevents the belt from running off sideways or up against the supporting structure of the conveyor.
2. The Prior Art
Rigid reversing rods have been commonly used in connection with devices for channeling conveyed materials at an acute angle into or out of the conveying track of a belt conveyor. The friction of the conveyor belt on the reversing rods generates heat, which is transferred unevenly onto the strands of the belt. This may result in nonuniform tension of the belt, which causes it to run off sideways until it comes into contact with the supporting framework of the device.
In order to keep the heating of the reversing rods low, the belt is not tightened when it is mounted, or it is tightened only slightly. Running sideways against the supporting frame causes the belt to bulge. Furthermore, the belt material, and in particular the polyester fabric contained therein, shrinks with rising temperatures. This may result in a disproportionate and uneven rise in the belt tension, and may even lead to a total breakdown of the conveyor.
For conveyor belts that have a tendency to run off course sideways, it is known to employ a guide roller to counteract lateral run-off. The guide roller acts only on a surface of the lower strand of the belt. This is the surface, which after the belt has been reversed into the upper strand, carries the stock being conveyed. This guide roller is swingable in the plane of the belt by a few degrees. With a guide roller of the known type, sensor bars are rigidly connected with it and are arranged upstream of and apart from the guide roller. The guide rollers are arranged on both sides of the belt. If an edge of the belt runs against the sensor bar associated with it, the guide roller is swivelled by the contact pressure of the belt. The guide roller rolls with a motion inclined relative to the running direction of the belt, which leads to forces of reaction. These forces have a component acting transverse to the direction of the belt, and lead to a resetting of the belt.
In addition, guide rollers driven by external force are known. These rollers can be adjusted, i.e., swivelled, via contactless scanning devices such as light barriers or capacitive sensors with the help of pneumatically operating devices or electric motors.
The known systems, however, are not suitable for conveyor belts having almost no tension, such as with a device for channeling conveyed goods into and out of a conveyor line as shown in European Patent No. EP 0 678 464 A1. Loose belts with such low tension are capable of transmitting only very low guide roller forces, which are insufficient for resetting a belt running off course. Furthermore, adequate transverse stiffness is missing, so that transmission of the laterally directed resetting forces is made more difficult. Therefore, the known guide roller devices cannot be used with a very flexible belt and are limited to stiff and tightened belts for systems that transport bulk materials.